1. Field of Invention
The present invention relates to a multi-layer thermoelectric module and a fabrication method thereof. More particularly, the present invention relates to a multi-layer thermoelectric module and a method for fabricating the multi-layer thermoelectric module using a solid-liquid interdiffusion jointing technique.
2. Description of Related Art
A thermoelectric material may use a temperature difference to generate electric current, generate electricity by recycling waste heat, or use electric current to cause temperature difference for achieving an object of active cooling for heat dissipation, which is of special meaning to the topics in modern electronics, energy and environmental protection.
However, a method for fabricating a conventional mono-layer or multi-layer thermoelectric module often adopts a low melting-point solder alloy soldering technique, or a high melting-point filler alloy brazing technique, in which a process temperature of the soldering method is relatively low, and an operating temperature of the fabricated thermoelectric module cannot be higher than the melting point of the solder alloy. Generally speaking, some moderate or low temperature thermoelectric materials have the most efficient thermoelectric conversion efficiency temperature which is already higher than the melting points of common solder alloys. Therefore, the soldering method is completely not applicable to the fabrication of thermoelectric module.
Besides, the filler alloy used by the brazing method for fabricating a thermoelectric module has a higher melting point. In the fabricated thermoelectric module, the brazed points can sustain a higher operating temperature, but the process temperature is also higher, in which the thermal stress generated therein may damage the thermoelectric module or cause thermoelectric material to fail.
Furthermore, when fabricating the multi-layer thermoelectric module of two or three layers, the conventional soldering or brazing technique also faces another problem, which is, when a second layer of thermoelectric module is fabricated after a first layer of thermoelectric module is completed, the solder-joint alloy or the brazing filler alloy of the first layer of thermoelectric module is melted to cause the joint surface to be detached or displaced. In order to solve the problem, in one method, the first layer of thermoelectric module may be fabricated by a brazing method, and the second layer of thermoelectric module may be fabricated by another brazing method with a lower process temperature or by using another solder alloy of which the melting point is lower than the temperature for fabricating the first layer of thermoelectric module. However, this method may result in the problem of low production efficiency. Another method is to joint two or three layers of thermoelectric unit with a metal electrode at one single temperature to form a multi-layer thermoelectric module, but the method has a high risk of failure, thus resulting in a low yield of the thermoelectric module process.
In view of this, there is a need to provide a multi-layer thermoelectric module and a method for fabricating the multi-layer thermoelectric module to improve the defects of the conventional thermoelectric module and a method of connecting a thermoelectric unit to a metal electrode.